Get a new visa in Vietnam

You can extend it 2 times after the first entry 

http://xnc.congan.com.vn/vietkieu-nuocn … 72397/view

Here is the entry link about how to get new visa from Cong An ( Police ) website. Hope it's useful for you ( Use Google translate into English )

Day trip to Cambodia or Thailand?

Should be able to stay up to 9 months total without leaving the country. Maybe longer with the right visa agent but could be a bit dodgy as there have been random anecdotal reports online of people getting one year visas from agents (or being able to renew them far beyond the stated 9 month limit) only to later have their visas cancelled for unexplained reasons. Personally I choose to leave every nine months...

I would these days steer clear of agencies that claim to be able to get you a one year or two year visa. This is normally done by charging you a few hundred dollars which is shared with a company which makes a false statement about your employment status with them. If you get caught the immigration people here can ban you from Vietnam for three years or more.

If you get married to a Vietnamese person (I just did) then things are slightly different. You go and get a load of forms signed by the police at your local police station. They will look at your marriage certificate and you will have to supply a photo copy. They will then register you as living at the address you gave them and:

a. If you are living in rented accommodation, ask to see your Landlords / Tenants Record Book.
b. If you are living in property that you own, there is no requirement for a. above.

You then toddle off to the immigration department with your passport and all the bits of paper and they then give you a 5 year "visa", however, you have to go to the immigration dept every three months for your visa to be reconfirmed. There is no charge either for the 5 year "visa", or for the 3 monthly confirmation and there is no requirement to leave the country every 9 months.

Interestingly, I returned to Saigon from a trip abroad on 26 Sept and my visa was due renewal on 5 Oct, so had I not been abroad I would have been leaving the country to get my visa extended within a few days anyway. When I explained to the immigration lady at the airport that I had just got married to a Vietnamese lady and that we would be applying for a "marriage visa", she very kindly extended my existing visa by 14 days for free, "to give me time to complete my marriage visa application".

It is obligated to come back your country to renew your visa.